Spl Deg Research Articles

Polarization rotation and the third Stokes parameter: the effects of spacecraft attitude and Faraday rotation

The third Stokes parameter of ocean surface brightness temperatures measured by the WindSat instrument is sensitive to the rotation angle between the polarization vectors at the ocean surface and the instrument. This rotation angle depends on the spacecraft attitude (roll, pitch, yaw) as well as the Faraday rotation of the electromagnetic radiation passing through the Earth's ionosphere. Analyzing the WindSat antenna temperatures, we find biases in the third Stokes parameter as function of the along-scan position of up to 1.5 K in all feedhorns. This points to a misspecification of the reported spacecraft attitude. A single attitude correction of -0.16/spl deg/ roll and 0.18/spl deg/ pitch for the whole instrument eliminates all the biases. We also study the effect of Faraday rotation at 10.7 GHz on the accuracy of the third Stokes parameter and the sea surface wind direction retrieval and demonstrate how this error can be corrected using values from the International Reference Ionosphere for the total electron content when computing Faraday rotation.

Organic "Wafer-Scale" packaged miniature 4-bit RF MEMS phase shifter

This paper presents for the first time a 4-bit microelectromechanical systems (MEMS) phase shifter fabricated on, integrated, and packaged into an organic flexible low-permittivity material. A microstrip switched-line phase shifter has been optimized at 14 GHz for small size and excellent performance. In addition, the MEMS phase shifter was packaged in an all-organic flexible low-permittivity liquid-crystal polymer (LCP) package. The improved geometry of the reduced size phase shifter is 2.8 times smaller than a traditional switched-line phase shifter and is much less lossy. For the 4-bit phase shifter, the worst case return loss is greater than 19.7 dB and the average insertion loss is less than 0.96 dB (0.24 dB/bit or 280/spl deg//dB). The average phase error is only 3.96/spl deg/. It has been demonstrated that the addition of the LCP package has a negligible effect on the phase-shifter performance, but will enable the device to remain flexible and protected against various environmental conditions.

Scanning Micromirrors Fabricated by an SOI/SOI Wafer-Bonding Process

MEMS scanning micromirrors have been proposed to steer a modulated laser beam in order to establish secure optical links between rapidly moving platforms. An SOI/SOI wafer-bonding process has been developed to fabricate scanning micromirrors using lateral actuation. The process is an extension of established SOI technology and can be used to fabricate stacked high-aspect-ratio structures with well-controlled thicknesses. Fabricated one-axis micromirrors scan up to 21.8/spl deg/ optically under a dc actuation voltage of 75.0 V, and have a resonant frequency of 3.6 kHz. Fabricated two-axis micromirrors scan up to 15.9/spl deg/ optically on the inner axis at 71.8 V and 13.2/spl deg/ on the outer axis at 71.2 V. The micromirrors are observed to be quite durable and resistant to shocks. Torsional beams with T-shaped cross sections are introduced to replace rectangular torsional beams in two-axis MEMS micromirrors, in order to reduce the cross-coupling between the two axial rotations. Fabricated bidirectional two-axis micromirrors scan up to /spl plusmn/7/spl deg/ on the outer-axis and from -3/spl deg/ to 7/spl deg/ on the inner-axis under dc actuation.

An Untethered, Electrostatic, Globally Controllable MEMS Micro-Robot

We present an untethered, electrostatic, MEMS micro-robot, with dimensions of 60 /spl mu/m by 250 /spl mu/m by 10 /spl mu/m. The device consists of a curved, cantilevered steering arm, mounted on an untethered scratch drive actuator (USDA). These two components are fabricated monolithically from the same sheet of conductive polysilicon, and receive a common power and control signal through a capacitive coupling with an underlying electrical grid. All locations on the grid receive the same power and control signal, so that the devices can be operated without knowledge of their position on the substrate. Individual control of the component actuators provides two distinct motion gaits (forward motion and turning), which together allow full coverage of a planar workspace. These MEMS micro-robots demonstrate turning error of less than 3.7/spl deg//mm during forward motion, turn with radii as small as 176 /spl mu/m, and achieve speeds of over 200 /spl mu/m/sec with an average step size as small as 12 nm. They have been shown to operate open-loop for distances exceeding 35 cm without failure, and can be controlled through teleoperation to navigate complex paths. The devices were fabricated through a multiuser surface micromachining process, and were postprocessed to add a patterned layer of tensile chromium, which curls the steering arms upward. After sacrificial release, the devices were transferred with a vacuum microprobe to the electrical grid for testing. This grid consists of a silicon substrate coated with 13-/spl mu/m microfabricated electrodes, arranged in an interdigitated fashion with 2-/spl mu/m spaces. The electrodes are insulated by a layer of electron-beam-evaporated zirconium dioxide, so that devices placed on top of the electrodes will experience an electrostatic force in response to an applied voltage. Control waveforms are broadcast to the device through the capacitive power coupling, and are decoded by the electromechanical response of the device body. Hysteresis in the system allows on-board storage of n=2 bits of state information in response to these electrical signals. The presence of on-board state information within the device itself allows each of the two device subsystems (USDA and steering arm) to be individually addressed and controlled. We describe this communication and control strategy and show necessary and sufficient conditions for voltage-selective actuation of all 2/sup n/ system states, both for our devices (n=2), and for the more general case (where n is larger.).

A Monolithic 6 GHz Quadrature Frequency Doubler With Adjustable Phase Offset

A 6 GHz frequency doubler with quadrature outputs generated from a differential single phase input is presented. The phase offset between the in-phase and quadrature outputs can be digitally controlled in linear steps for use in an automated calibration algorithm. The design nominally achieves standard deviations in quadrature phase error and amplitude balance of 0.4/spl deg/ and 0.1dB, respectively. This is demonstrated with a single sideband (SSB) mixer that realizes an average uncalibrated sideband rejection of 48.2 dB which improves to 55.8 dB post-calibration under nominal conditions.

Stability of amorphous-silicon TFTs deposited on clear plastic substrates at 250/spl deg/C to 280/spl deg/ C

Amorphous-silicon (a-Si) thin-film transistors (TFTs) were fabricated on a free-standing new clear plastic substrate with high glass transition temperature (T/sub g/) of >315/spl deg/ C and low coefficient of thermal expansion of <10 ppm/ /spl deg/ C. Maximum process temperatures on the substrates were 250/spl deg/C and 280/spl deg/C, close to the temperatures used in industrial a-Si TFT production on glass substrates. The first TFTs made at 280/spl deg/C have dc characteristics comparable to TFTs made on glass. The stability of the 250/spl deg/C TFTs on clear plastic is approaching that of TFTs made on glass at 300/spl deg/C-350/spl deg/C. TFT characteristics and stability depend only on process temperature and not on substrate type.

1.55-/spl mu/m ridge DFB laser and electroabsorption Modulator integrated with buried-ridge-stripe dual-waveguide spot-size converter output

A 1.55-μm ridge distributed feedback laser and electroabsorption modulator monolithically integrated with a buried-ridge-stripe dual-waveguide spot-size converter (SSC) at the output port for low-loss coupling to a cleaved single-mode optical fiber was fabricated by means of selective area growth, quantum-well intermixing, and dual-core technologies. These devices exhibit threshold current of 28 mA, 3-dB modulation bandwidth of 12.0 GHz, modulator extinction ratios of 25.0-dB dc. The output beam divergence angles of the SSC in the horizontal and vertical directions are as small as 8.0/spl deg/×12.6/spl deg/, respectively, resulting in 3.2-dB coupling loss with a cleaved single-mode optical fiber.

Speed control of a new disc-type ultrasonic motor by using current controller

The rotational speed of an ultrasonic motor is related to the vibration speed of its stator. Because drift of the piezostator characteristics will cause variation of the motor speed, a controller is thus necessary in order to produce a constant output speed. Variations of the motor output characteristics will also make it very difficult to obtain the efficiency of the motor. This paper points out the origins of possible drifts in a new disc-type piezoelectric ultrasonic motor which has three nonequal-triangular (120/spl deg/-90/spl deg/-150/spl deg/) fixed points near the edge. The frequency behavior of the proposed motor and its consequences on speed control scheme are discussed. The speed control scheme is implemented by using current modulation, so the rotational speed will be kept constant.

Long range wireless characterisation of 2.4 GHz SAW-based pressure sensor using network analyser

A 2.4 GHz range surface acoustic wave (SAW)-based pressure sensor was fabricated on a 41/spl deg/ YX LiNbO/sub 3/ substrate for a mechanical compression force measurement. For the first time, fabricated sensors were characterised wirelessly using the network analyser. Electron beam lithography was used for fine line patterning. Metal ground shielding was covered all over the cavity to reduce a coupling loss of the propagating SAW to the surrounding atmosphere. Equivalent circuit model and finite element methods were used to determine optimal design parameters. The three sharp peaks were obtained from three reflectors. As a mechanical force was applied to the piezoelectric diaphragm, the diaphragm was bended, resulting in the phase shifts of the reflected peaks. Obtained sensitivity was 2.9/spl deg//kPa.

Recovering 3D human pose from monocular images

We describe a learning-based method for recovering 3D human body pose from single images and monocular image sequences. Our approach requires neither an explicit body model nor prior labeling of body parts in the image. Instead, it recovers pose by direct nonlinear regression against shape descriptor vectors extracted automatically from image silhouettes. For robustness against local silhouette segmentation errors, silhouette shape is encoded by histogram-of-shape-contexts descriptors. We evaluate several different regression methods: ridge regression, Relevance Vector Machine (RVM) regression, and Support Vector Machine (SVM) regression over both linear and kernel bases. The RVMs provide much sparser regressors without compromising performance, and kernel bases give a small but worthwhile improvement in performance. The loss of depth and limb labeling information often makes the recovery of 3D pose from single silhouettes ambiguous. To handle this, the method is embedded in a novel regressive tracking framework, using dynamics from the previous state estimate together with a learned regression value to disambiguate the pose. We show that the resulting system tracks long sequences stably. For realism and good generalization over a wide range of viewpoints, we train the regressors on images resynthesized from real human motion capture data. The method is demonstrated for several representations of full body pose, both quantitatively on independent but similar test data and qualitatively on real image sequences. Mean angular errors of 4-6 degrees are obtained for a variety of walking motions.

Analysis of surface roughness and morphology of first-year sea ice melt ponds: implications for microwave scattering

Variations in wind forcing over summer first-year sea ice (FYI) melt ponds occur at hourly to weekly scales and are a significant contributor to microwave backscatter (/spl sigma//spl deg/) variability observed from spaceborne synthetic aperture radar (SAR) platforms (e.g., ENVISAT-ASAR and RADARSAT-1). This variability impairs our ability to use SAR to derive information on summer sea ice thermodynamic state and energy balance parameters such as albedo and melt pond fraction. The surface roughness contribution of FYI melt ponds in the Canadian Arctic Archipelago to like-polarized, C-band /spl sigma//spl deg/ estimates is analyzed through a spectral and statistical analysis of surface wave height profiles for varying wind speeds, upwind fetch lengths, and melt pond depths. A unique derivation of melt pond surface wave height spectra is presented based on digital video of melt pond surface wave trains. Significant scale surface roughness was observed even at wind speeds of 3 m/spl middot/s/sup -1/, resulting in small perturbation model estimates of /spl sigma//spl deg/ (HH) ranging from -5 dB at 20/spl deg/ incidence to -22 dB at 50/spl deg/ incidence. Results from a multivariate linear regression analysis show that 53.5% of observed variance in /spl sigma//spl deg/ (HH or VV) can be explained by wind speed, upwind fetch from melt pond edges, and melt pond depth, with no appreciable difference in the relative contribution of explanatory variables. Modeled omnidirectional /spl sigma//spl deg/ as a function of wind speed and incidence angle for 100-m transects collected throughout the melt pond season act to elaborate the role of fetch and depth, as well as the modulating effect of hummocks, on /spl sigma//spl deg/.

Gimbal-less MEMS two-axis optical scanner array with high fill-factor

In this paper, we report on a MEMS-based two-axis optical scanner array with a high fill factor (>96%), large mechanical scan angles (/spl plusmn/4.4/spl deg/ and /spl plusmn/3.4/spl deg/), and high resonant frequencies (20.7 kHz). The devices are fabricated using SUMMiT-V, a five-layer surface-micromachining process. High fill factor, which is important for 1/spl times/N/sup 2/ wavelength-selective switches (WSSs), is achieved by employing crossbar torsion springs underneath the mirror, eliminating the need for gimbal structures. The proposed mirror structure can be readily extended to two-dimensional (2-D) array for adaptive optics applications. In addition to two-axis rotation, piston motion with a stroke of 0.8 /spl mu/m is also achieved. [1496].

Carrier synchronization for 3- and 4-bit-per-symbol optical transmission

We investigate carrier synchronization for coherent detection of optical signals encoding 3 and 4 bits/symbol. We consider the effects of laser phase noise and of additive white Gaussian noise (AWGN), which can arise from local oscillator (LO) shot noise or LO-spontaneous beat noise. We identify 8- and 16-ary quadrature amplitude modulation (QAM) schemes that perform well when the receiver phase-locked loop (PLL) tracks the instantaneous signal phase with moderate phase error. We propose implementations of 8- and 16-QAM transmitters using Mach-Zehnder (MZ) modulators. We outline a numerical method for computing the bit error rate (BER) of 8- and 16-QAM in the presence of AWGN and phase error. It is found that these schemes can tolerate phase-error standard deviations of 2.48/spl deg/ and 1.24/spl deg/, respectively, for a power penalty of 0.5 dB at a BER of 10/sup -9/. We propose a suitable PLL design and analyze its performance, taking account of laser phase noise, AWGN, and propagation delay within the PLL. Our analysis shows that the phase error depends on the constellation penalty, which is the mean power of constellation symbols times the mean inverse power. We establish a procedure for finding the optimal PLL natural frequency, and determine tolerable laser linewidths and PLL propagation delays. For zero propagation delay, 8- and 16-QAM can tolerate linewidth-to-bit-rate ratios of 1.8/spl times/10/sup -5/ and 1.4/spl times/10/sup -6/, respectively, assuming a total penalty of 1.0 dB.

Surface- and bulk- micromachined two-dimensional scanner driven by angular vertical comb actuators

In this paper, we present the design, fabrication, and measurements of a two-dimensional (2-D) optical scanner with electrostatic angular vertical comb (AVC) actuators. The scanner is realized by combining a foundry-based surface-micromachining process (Multi-User MEMS Processes-MUMPs) with a three-mask deep-reactive ion-etching (DRIE) postfabrication process. The surface-micromachining provides versatile mechanical design and electrical interconnect while the bulk micromachining offers high-aspect ratio structures leading to flat mirrors and high-force, large-displacement actuators. The scanner achieves dc mechanical scanning ranges of /spl plusmn/6.2/spl deg/ (at 55 Vdc) and /spl plusmn/4.1/spl deg/ (at 50 Vdc) for the inner and outer gimbals, respectively. The resonant frequencies are 315 and 144 Hz for the inner and the outer axes, respectively. The 1-mm-diameter mirror has a radius of curvature of over 50 cm. [1454].

A High Precision Resolver-to-DC Converter

A newly developed resolver converter, providing a pseudolinear voltage proportional to the shaft angle, is presented. This converter is based on a new concept involving the absolute values of the demodulated sine and cosine resolver signals together with a dedicated linearization technique. The converter enables instantaneous determination of the mechanical angle with a theoretical error of nonlinearity below 0.011/spl deg/ over the 360/spl deg/ range. The practical performance of this converter is compared to that of a 10/sup 5/ pulses per revolution optical encoder arrangement. The theory of operation, computer simulation, full circuit details, and experimental results are given.

All-digital PLL and transmitter for mobile phones

We present the first all-digital PLL and polar transmitter for mobile phones. They are part of a single-chip GSM/EDGE transceiver SoC fabricated in a 90 nm digital CMOS process. The circuits are architectured from the ground up to be compatible with digital deep-submicron CMOS processes and be readily integrateable with a digital baseband and application processor. To achieve this, we exploit the new paradigm of a deep-submicron CMOS process environment by leveraging on the fast switching times of MOS transistors, the fine lithography and the precise device matching, while avoiding problems related to the limited voltage headroom. The transmitter architecture is fully digital and utilizes the wideband direct frequency modulation capability of the all-digital PLL. The amplitude modulation is realized digitally by regulating the number of active NMOS transistor switches in accordance with the instantaneous amplitude. The conventional RF frequency synthesizer architecture, based on a voltage-controlled oscillator and phase/frequency detector and charge-pump combination, has been replaced with a digitally controlled oscillator and a time-to-digital converter. The transmitter performs GMSK modulation with less than 0.5/spl deg/ rms phase error, -165 dBc/Hz phase noise at 20 MHz offset, and 10 /spl mu/s settling time. The 8-PSK EDGE spectral mask is met with 1.2% EVM. The transmitter occupies 1.5 mm/sup 2/ and consumes 42 mA at 1.2 V supply while producing 6 dBm RF output power.

Suppression of numerical anisotropy and dispersion with optimized finite-difference time-domain methods

To reduce numerical dispersion in finite-difference time-domain (FDTD) methods, large computational stencils are often used. This paper proposes an optimized two-dimensional method by weighting the (2,4) stencil and the neighborhood stencil. After obtaining the amplification factor and the numerical dispersion relation, the optimal value of the weight parameter is obtained to minimize the numerical dispersion at a designated frequency. The anisotropy, dispersion error and the accumulated phase errors are greatly reduced over a broad bandwidth. Both the maximum anisotropy and the maximum dispersion error are 8.9/spl times/10/sup -5/, and the accumulated phase error is 0.002367/spl deg/ per cell, respectively, for a broad band of frequencies if optimized at 10 cells per wavelength. Numerical experiments are performed which show very good agreement with theoretical analysis. The time step size bound is the same as for Yee's FDTD.

A method for aligning trans-tibial residual limb shapes so as to identify regions of shape change

Quantification of the change in shape of a residual limb over time is relevant to the fitting of an external prosthesis. Three algorithms were developed and evaluated to align residual limb shapes: iterative closest points (ICP), mean absolute difference, and weighted surface normals/mean absolute difference. Evaluations were conducted by aligning residual limb shapes with known deformations and transformations with their original shapes. Results showed that ICP did not perform well in that it tended to favor a global distribution of local shape difference rather than localization of the error. The mean absolute difference algorithm performed well as long as the shape difference was localized to one region. Weighted mean surface normals/absolute difference provided the best alignment results, performing well both if shape changes were localized and if they were globally distributed. Mean alignment errors for this method were less than 0.285 mm for each of the three translation directions and less than 0.357 degrees for each of the three rotation directions. This algorithm could be helpful to patients, prosthetists, and researchers developing treatments to overcome the detrimental fitting effects of residual limb shape change.

Hot pixel annealing behavior in CCDs irradiated at -84/spl deg/C

A Hubble space telescope wide field camera 3 e2v CCD was irradiated while operating at -84/spl deg/C and the dark current studied as a function of temperature while the charge coupled device was warmed to a sequence of temperatures up to a maximum of +30/spl deg/C. The device was then cooled back down to -84/spl deg/ and remeasured. Hot pixel populations were tracked during the warm up and cool down. Hot pixel annealing began below -40/spl deg/C and the anneal process was largely completed by the time the detector reached +20/spl deg/C. There was no apparent sharp annealing temperature. Although a large fraction of the hot pixels fell below the threshold to be counted as a hot pixel, they nevertheless sustained a higher leakage rate than the remaining population. The mechanism for hot pixel annealing is not presently understood. Room temperature irradiations do not adequately characterize the hot pixel distributions for cooled applications.

Temperature-insensitive tilt sensor with strain-chirped fiber Bragg gratings

A novel tilt sensor with three fiber Bragg gratings (FBGs) has been demonstrated. It can detect the magnitude as well as the direction of the inclination from the horizontal direction by measuring the reflected optical powers of the FBGs, whose bandwidths vary with the inclination, directly. The experimental results show that it is insensitive to temperature. The measurement accuracy of /spl plusmn/0.13/spl deg/ and resolution of 0.02/spl deg/ have been achieved.